The invention described herein was made by employees of the United States Government and may be manufactured and used by or for the Government or Government purposes without the payment of any royalties thereon or therefore.
In general, the present invention is directed to sensors. In particular, the present invention is directed to high temperature semiconductor sensors. Specifically, the present invention is directed to silicon carbide sensors and packaging sufficient to withstand high vibration and high temperature environments.
Computer simulations of engine behavioral parameters have led to computerization of the design and production of new turbine engines. With the improvements in sensor technology, engine designs for the purpose of increasing aviation safety, efficient energy management and improved emission control can now be easily obtained. To facilitate this desirable acquisition of information, computer simulations are performed using codes that are generated by Computational Fluid Dynamics (CFD). Results from these codes are useful in determining design changes that should be incorporated into the engine design. It is therefore crucial that these CFD codes be very accurate in predicting the behavior of the engine. Validation of the accuracy of the CFD codes requires the direct measurement of the engines behavioral parameters such as pressure, flow and temperature. Results of these measured parameters are compared against the ones from CFD calculations. Accordingly, by utilizing direct measurement it is believed that further improvement of the codes can be obtained, thereby minimizing errors in simulations and increasing the confidence of using the CFD codes.
Sensor use to measure the conditions inside an engine are currently limited to the low temperature sections wherein low temperature is defined as anything less than 200xc2x0 C. This limitation makes it difficult and expensive to validate CFD codes generated with respect to the higher temperature sections ( greater than 200.xc2x0 C.). In cases where the high temperature sections are monitored, the results are largely unreliable due to limitations imposed by currently known sensors and the properties of the package material which carry the sensor.
Generally, packaging components have different material properties than the sensors that they carry. As a result of the mismatch created by the differences in the coefficients of thermal expansion for the sensor and its packaging, undesirable transient thermomechanical stresses are induced on the sensor. These stresses lead to creep and fatigue that cause gradual deviation from true measurement and eventual failure of the sensor. It is believed that the current packaging methods lack the required precision placement of a cantilever beam which is used as the sensing component. As a result of the lack of precision alignment, the beam is often misaligned which leads to the introduction of undesirable stresses when the beam is inserted into the flow field. Also, because the beam is not precisely placed on a clamped edge, maximum strain is not transferred to the gauges disposed on the beam leading to reduced sensitivity. The lack of consistency in the placement of the cantilever beam means that readings from one sensor to another will vary. Moreover, the relatively large area of the cantilever beam used in known prior art sensors creates turbulence in the flow field that prevents measurement of actual flow parameters. Additionally, the materials used in currently known packaging, including the sensor, which are generally silicon, are limited to a low temperature environment.
Yet another drawback of existing sensor devices used in high temperature and high vibration environments is that they use wire bonding technologies. The bond wires are suspected to act as antennas that receive spurious electromagnetic noise generated in such an environment. It is believed that this noise interacts with the actual measured signals and causes them to be inaccurate.
Based upon the foregoing it is therefore a primary object of the present invention to provide a silicon carbide high temperature anemometer and method for assembling the same.
Another object of the present invention, which shall become apparent as the detailed description proceeds, is achieved by a high temperature anemometer, comprising a pair of substrates, one of the substrates having a plurality of electrodes on a facing surface, the other of the substrates having a sensor cavity on a facing surface; and a sensor received in the sensor cavity, the sensor having a plurality of bond pads, wherein the bond pads contact the plurality of electrodes when the facing surfaces are mated with one another.
Other aspects of the present invention are attained by a sensor comprising a housing having a package cavity therethrough; a sensor package received in the housing, the sensor package having a silicon carbide cantilever beam sensor extending outwardly from the housing.
Still another object of the present invention is attained by a method for assembling an anemometer, comprising providing a cantilever beam having a plurality of bond pads on one side thereof providing a first substrate and a second substrate, each substrate being of the same material as the cantilever beam; etching the first substrate with a plurality of trenches and a cavity; passivating both of the substrates; disposing a plurality of electrodes on the second substrate; positioning the cantilever beam in the cavity; positioning a plug-in pin in each of the trenches; and mating the first substrate with the second substrate so that the plug-in pins and the bond pads are in intimate contact with the plurality of electrodes.
These and other objects of the present invention, as well as the advantages thereof over existing prior art forms, which will become apparent from the description to follow, are accomplished by the improvements hereinafter described and claimed.